1. Field of the Invention
The present invention relates to a developing apparatus and a process cartridge containing at least such developing apparatus, adapted for use in an image forming apparatus such as an electrophotographic copying apparatus or an electrophotographic printer.
2. Related Background Art
In an image forming apparatus performing an electrophotographic process, an electrostatic latent image formed on an image bearing member is visualized as a toner image by a developing apparatus. Among such developing apparatus there have been proposed one-component dry developing apparatus of various types, but, in any of these apparatus, it is difficult to form a thin layer of toner constituting the one-component developer on the developer bearing member.
However, improvement in resolution and clearness of the image is now being desired, the development of the method for forming a thin toner layer and the apparatus therefor are essential and there have been made several proposals.
For example Japanese Patent Application Laid-open No. 54-43038 proposes an apparatus in which a metal or rubber elastic blade is abutted against a developing sleeve constituting a developer bearing member to regulate the toner layer by passing the toner between the elastic blade and the developing sleeve, thereby a thin toner layer is formed on the developing sleeve and the toner is provided with sufficient triboelectricity by friction in the contacting portion.
In such case, if the above-mentioned elastic blade regulates non-magnetic toner, there is separately required a toner supply member for supplying the toner onto the developing sleeve. This is because the non-magnetic toner cannot be supplied by magnetic force, though magnetic toner can be supplied onto the developing sleeve by the magnetic force of the magnet provided in the developing sleeve.
For this reason, there has been proposed a developing apparatus 50 shown in FIG. 18. In this conventional developing apparatus 50, in a developer container 54 containing non-magnetic toner 53 as the one-component developer, an elastic roller 55 composed of a foamed member such as of polyurethane foam or sponge or fur brush is provided abutting against a developing sleeve 52 at the upstream position, in the rotating direction thereof, of an elastic blade 51, and is rotated in a direction D to feed the toner 53 onto the developing sleeve 52.
The toner 53 fed onto the developing sleeve 52 is supplied, by the rotation thereof, to the contact (abutting) area between the elastic blade 51 and the developing sleeve 52, thus being formed into a thin layer, and is used for developing the electrostatic latent image borne on a photosensitive drum 1 serving as the image bearing member. Then, the toner 53 not consumed in the image development but remaining on the developing sleeve 52 is peeled off by the elastic roller 55 while new toner 53 is fed onto the developing sleeve 52 as described in the foregoing, and these operations are repeated. If the developing sleeve 52 is composed of a metallic material, the elastic blade 51 of a thin metal plate is no desirable in consideration of the abrasion of the developing sleeve, and it has to be formed with a rubber material such as urethane rubber or silicone rubber or the like in order to obtain a satisfactory thin layer of toner.
Such configuration allows a satisfactory thin layer of non-magnetic toner to be formed on the developing sleeve. However, in comparison with the magnetic developing apparatus employing magnetic toner and capable of easily holding toner on the surface of the developing sleeve by the function of the magnetic field, it becomes difficult to prevent the leakage of toner 53 from the developing apparatus 50 because the non-magnetic toner does not allow the magnetic attractive force. To be utilized more specifically, the developing sleeve 52 can only hold the toner which has passed the abutting area between the elastic blade 51 and the developing sleeve 52 and has been given sufficient triboelectricity, with the results that toner may easily leak from the lower part or end portions of the developing sleeve 52 to the exterior, resulting in smear of the interior of the image forming apparatus with toner.
For this reason, a flexible developer sealing member (hereinafter simply called seal member) 56 abutting against the developing sleeve 52 with small pressure is provided at the toner recovering portion in the lower part of the developer container 54, in order to permit the passage of the toner not used in the image development and to prevent leakage of the toner 53 from the lower part of the developer container 54.
The above-described developing apparatus has been employed in compact copying machines and page printers, but is recently utilized as a developing unit or a process cartridge integrally containing the developing apparatus and the photosensitive drum eventually with the cleaner and/or the charging device.
In the above-mentioned cartridge or developing unit, the developing apparatus is provided with various sealings since the toner may leak by the impact given in the developing apparatus at the replacement thereof. In particular, in an aperture for collecting the unused toner or the developing sleeve 52 into the developing apparatus, a seal member 56 is provided for preventing the leakage of toner from the developing apparatus without hindering collecting of toner.
As shown in FIG. 19, the seal member 56 is composed of a strip-shaped sheet, which is wider than the developing area of the developing sleeve 52, and is fixed at an end to a lower frame 57 of the developing apparatus and is in frictional contact at the free end by the elasticity thereof with the developing sleeve 52, along the rotating direction thereof. The seal member 56 is composed of a thin urethane rubber or a polycarbonate film of low rigidity or PET (polyethylene terephthalate) or the like. The seal member 56 bends toward the interior of the developing apparatus as indicated by an arrow in FIG. 20, thereby it does not hinder collecting of the toner. Also the seal member 56 is inclose contact with the developing sleeve 52 and or events toner blowing from the interior of the developing apparatus, thus preventing toner leakage.
However, when the developing operation is repeated many times with the conventional developing apparatus described above, the toner 53, having a high charge amount because of one-component non-magnetic toner, eventually charges the entire surface of the frame 57 and the developer container 54. Experimentally it is found that most of the frame 57 in the longitudinal direction thereof tends to be charged in a polarity opposite to that of the toner 53. Consequently, in such charged portion, under the application of the developing bias, there will result an electric field in a direction to strip the toner 53 from the developing sleeve 52 toward the seal member 56 at the toner collecting operation. Thus the toner 53 at the collecting operation remains on the seal member 56 and drops off to badly smear the interior of the image forming apparatus, thus resulting in so-called toner leakage.
Also, when the developing operation is repeated many times with the conventional developing apparatus described above, there will result impact and vibration in the image forming apparatus, and such impact and vibration are applied to the developing apparatus to deform the frame 57 and the seal member 56 provided thereon, thereby generating a gap in the contact area with the developing sleeve 52 and eventually resulting in severe smear of the interior of the image forming apparatus.